The invention relates to a method for activating an output stage, with a first and a second circuit-breaker, of a safety system for vehicle occupants having at least one electrically operated triggering means, wherein the first circuit-breaker connects the triggering means with an operating potential and the second circuit-breaker with a reference potential (ground) and a current detector is assigned to each circuit-breaker.
Furthermore, the invention also relates to a device for performing the method.
Increasingly, motor vehicles incorporate safety systems such as airbags, belt tighteners or roll sensors serving as a protection for vehicle occupants. These are safety-critical systems on which exacting demands are placed with respect to functional reliability. Examples of triggering means for these safety systems are ignition pills for belt tightener and airbag systems as well as relays for switching other safety systems. Such triggering means are usually arranged in a load circuit, containing in addition high and low switches and possibly mechanical switches, controlled by an output stage.
If the conditions for triggering a safety system are provided, it is important that the triggering means, such as ignition pills of airbag gas generators, be activated for a sufficient period of time with an appropriate safety factor. The activation of an output stage generates a flow of current in the load circuit so that ignition pills are heated up by the flow of current and thus start a pyrotechnic reaction. The ignition pills tend, however, to form parallel connections during or after ignition and the safety time factor provided for reliable activation of the ignition pills represents a danger for the output stage in the event of a parallel connection with rising current because if a fault occurs the output stage operates on a short circuit and is thus heavily loaded. In normal operation, the flow of current through the load circuit is interrupted by activation of the ignition pill and thus limited to the response time of the ignition pill.